Integrated circuit chip packages are typically formed by mounting an integrated circuit chip on a lead frame and coupling these two elements together using wire bonding to form a package. The integrated circuit chip and lead frame are typically encapsulated after they are coupled together.
As shown in FIG. 1, a lead wire 106, typically made of gold, silver, or copper, is fed through the capillary 104. The capillary 104 is affixed in a transducer 102 which provides ultrasonic energy transfer through the capillary 104 and through the free air ball 204 which creates a micro scrubbing during formation of the 1st bond 108 in the wirebonding process. In typical wire bonding tools the transducer 102 supplies ultrasonic energy at 60 kHz although transducers in some high frequency wire bonding tools supply ultrasonic energy at 90 kHz to 250 kHz.
The primary steps in the wire bonding process are illustrated in FIGS. 2A through 2F.
In FIG. 2A the lead wire 106 is extended below the bottom of the capillary 104. Electronic Flame Off with approximately 5,000 volts is then supplied to heat the wire causing it to melt and to form a free air ball 204 below the end of the capillary 104.
In FIG. 2B, the capillary 104 is lowered to bring the free air ball 204 into contact with a bond pad 200 of the integrated circuit. Pressure and ultrasonic energy is applied to form a ball bond 108 between the bond pad 200 and the lead wire 106.
As shown in FIG. 2C, a length of lead wire 106 is then fed through the capillary 104 and the capillary 104 is moved to position the lead wire 106 over the lead frame 202.
As shown in FIG. 2D, the capillary 104 is then lowered to bring the lead wire 106 into contact with the lead frame 202.
In FIG. 2E ultrasonic energy is applied to melt the lead wire 106 and form a stitch bond 112 between the bond wire 106 and the lead frame 202.
FIG. 2F illustrates a completed wire bond, where a ball bond 108 couples one end of the lead wire 106 to the bond pad 200 on the bond pad 200 of the IC and a stitch bond couples the other end of the lead wire 106 to the lead frame 202.